1. Field of the Invention
This invention relates generally to an electrical device for providing a data communications link between an electronic monitoring unit associated with each cell in a battery module and a battery system manager (BSM) and, more particularly, to an electrical device that provides capacitive coupling through integrated metal foils in each cell in a battery module to provide a data communications link between the integrated electronic monitoring unit in adjacent cells and a BSM.
2. Discussion of the Related Art
Electric vehicles are becoming more and more prevalent. These vehicles include hybrid vehicles, such as the extended range electric vehicles (EREV), that combine a battery and a main power source, such as an internal combustion engine, fuel cell system, etc., and electric only vehicles, such as the battery electric vehicles (BEV). These batteries can be different battery types, such as lithium-ion, nickel metal-hydride, lead-acid, etc. A typical high voltage battery system for an electric vehicle may include several battery cells electrically coupled in series to provide the vehicle power and energy requirements. The battery cells may be grouped into battery modules, where each module may include a certain number of cells, and where the cells in a module are electrically coupled in series and/or parallel. The number of cells in a module and the number of modules in a vehicle depends on battery technology and application. For example, for Li-Ion type battery modules it is common use to have twelve cells in series in a module. Different vehicles may have different battery designs that employ various trade-offs and advantages for a particular application.
As a result of many factors, such as cell self-discharge rate, internal cell resistance, electrical connections, battery aging, etc., the state-of-charge (SOC) of the cells in the battery may drift apart during operation of the battery over time. A battery management system (BSM) may be provided to monitor the voltage thresholds, impedance, state-of-health and state-of-charge of each battery cell and the temperature of the battery, and control how much the battery can be charged and discharged based on the state-of-charge of the maximum charged cell and the minimum charged cell. The battery cannot be used to provide power if the cell with the lowest state-of-charge drops below some minimum state-of-charge because that cell may become damaged, and the battery cannot be over-charged beyond some maximum state-of-charge for the cell with the highest state-of-charge because that cell may become overheated and damaged. Thus, a cell with a low state-of-charge may prevent the battery from being used even though the other cells may have a suitable or significant state-of-charge.
In one known vehicle battery design, each battery module includes a cell sensing board (CSB), where each cell in the module is electrically coupled to the CSB by an analog wire. The CSB receives analog voltage signals from each battery cell in the module and uses filtering circuits, multiplexers, analog-to-digital (A/D) converters, etc. to send the voltage signals on a digital wired communications link to the BSM. Because each cell in the battery modules has a voltage potential, such as 3-4 volts, a DC voltage shift occurs from one battery cell to an adjacent battery cell along the communications link as a result of that potential difference. It is known in the art to provide capacitors or transformers between two electrical connections to prevent DC current flow from one side of the capacitor to the other. Typically, an electrical twisted-pair of wires is provided in the communications link between the CSBs that include the capacitors or transformers that provide DC breaking so only the digital signals pass across the capacitor.
A new battery design has been investigated that eliminates the need for the CSBs in each battery module. Particularly, it has been proposed in the art to provide what are sometimes referred to as “smart cells” that include a low cost electronic monitoring unit integrated into the cell that includes electronics for monitoring the voltage and temperature of the cell, and to control the state-of-charge of individual cells by by-passing the cells using a switched resistor, also known as “passive balancing.” Particularly, each battery cell is equipped with an integrated electronic circuit that is part of the cell structure itself. Each electronic monitoring unit in each smart cell is part of the communications link from one cell to the next cell known as a chain topology so that the signals from each cell can be sent to the BSM. However, providing a capacitor, a connector and a twisted wire pair for each monitoring unit in the smart cell along the communications link is somewhat infeasible because of the number of connections that would be required.